The proposed project has the major objective to determine the biochemical, morphological, and physiological mechanisms that control the excitationeffector processes within the bioluminescent systems of coelenterates and other organisms. Biochemically we are examining the photoproteins responsible for the light emission, how they are packaged within cells, and their mechanisms of control at the cellular level. Morphologically we are attempting to determine the developmental patterns, movements and migrations of these fluorescent photocytes. We are also examining their ultrastructure for subcellular molecular arrangement, photocyte coupling to other cells, and general architecture. Physiologically we are examining the excitation system control on the luminescent photocytes and its relation to other excitation systems. We are also looking at the inherent circadian rhythms of luminescent activity in hydroids. All of these approaches are aimed at improving our knowledge of effector cells and excitation-effector coupling.